1. Field of the Invention
The present invention relates generally to digital information embedding devices and computer-readable recording media having a digital information embedding program recorded therein, and particularly to those capable of embedding digital watermark information for example of copyright information and user information in an exact digital content.
2. Description of the Background Art
As computer technology has been advanced, video, audio and other various information are more frequently digitized and thus used on computers. A digitized content does not degrade if it is copied. As such it is crucial to protect the copyright of the content. One method of protecting a copyright that is currently used is to add copyright information to a header of a content and read the information when the contents is used. FIGS. 9A and 9B schematically show an image having a content with a header having copyright information added thereto. With reference to FIG. 9A, the content includes an exact content such as an image and a header. With reference to FIG. 9B, the header has copyright information added thereto. This method is disadvantageous, however, since the copyright information is lost when the content is converted in a different format, an analog manner, or the like.
FIGS. 10A and 10B schematically show a method modifying an exact content to embed information. With reference to FIG. 10A, a content includes an exact content such as an image and a header. With reference to FIG. 10B, the exact content is modified to embed information in the exact content. This digital watermark technique has in recent years been attracting attention.
The digital watermark technique will now be briefly described. As described in Nikkei Electronics, No. 683, pp.100-107, a digital content, including audio and video data, has a portion which is not important to human senses, i.e., a redundant portion. In the technique such a redundant portion is noted and information such as copyright is embedded on a content in the form of noise. The embedded information is detected via characteristics of the method used to embed the information.
Digital watermark information is a noise on a content if the meaning carried by the information is not considered. As such, embedding information inevitably degrades the exact content. FIGS. 11A and 11B schematically show an image representing a content before it has information embedded therein, and an image representing the content after it has embedded therein information too much relative to the content, respectively. If information to be embedded in a content is large in amount relative to the content, a human sense can perceive degradation of the content in the form of noise, which is not desirable for digital watermark.
In contrast, if information too small relative to a content is embedded in the content, watermark information would readily be removed. FIGS. 12A and 12B schematically show an image representing a content before it has information embedded therein, and an image representing the content after it has embedded therein information too small relative to the content, respectively, and FIG. 12C shows the content after it is for example compressed or has noise removed. With the content having a small noise embedded and thus added thereto, if the content with information embedded therein as show in FIG. 12B is for example compressed or has noise removed, watermark information would be removed. As such, watermark information could not be detected in the content shown in FIG. 12C. This problem also similarly occurs if noise is added in a range limited to a redundant portion of a content.
Thus digital watermark information is required to be embedded with a level of degradation imperceptible through human senses and it is also required to be hardly removable. Accordingly, determining an appropriate degree of noise or information to be embedded in a content relative to the content, i.e., determining an appropriate degree to be applied to change the value of the content, is crucial in successfully embedding digital watermark information. Furthermore the degree of the information to be embedded in the content needs to be determined to accommodate the content receiving digital watermark information. Otherwise, the content, when it has digital watermark information embedded therein, would be significantly degraded or have the watermark information readily removed.
Thus a content needs to have a different degree of information embedded therein. In general, however, even a single content has therein portions having different properties. As such, if information is embedded in a content at a degree changed uniformly across the content, the content would on one hand have a portion allowing a variation to be readily perceived and on the other hand have a potion allowing a variation to be hardly recognized as watermark information. Accordingly, rather than it has a uniformly changed degree of information embedded therein, even a single content needs to have different degrees of information embedded therein for different portions thereof, such that if a portion of the content allows a variation to be readily perceived then it would have a small degree of information embedded therein whereas if a portion of the content hardly allows a variation to be readily perceived then it would have a large degree of information embedded therein.
One such method is disclosed in Japanese Patent Laying-Open No. 11-284836. This method uses a medical filter to determine a degree of information to be embedded. The method provides noise removal and in addition thereto high-precision edge enhancement to determine a feature value variation range perceptible through human senses.
In the above method, however, a content is subjected to noise removal and edge enhancement successively and thereafter has digital watermark information embedded therein. This inevitably involves a complicated process, requiring a negligibly long period of time to embed digital watermark information. Thus this method is not suitable for embedding information in a content dynamically when the content is displayed and reproduced.